The present invention relates generally to a method and apparatus for use in orthopedic surgery and more particular to a method and apparatus for providing a shell component incorporating a porous ingrowth material and liner for use during an orthopedic surgical procedure, particularly with respect to a prosthetic hip.
A natural hip joint may undergo degenerative changes due to a variety of etiologies. When these degenerative changes become so far advanced and irreversible, it may ultimately become necessary to replace a natural hip joint with a prosthetic hip. To replace the hip, a prosthetic hip may be affixed to the femur in one of many ways generally known in the art. In addition to replacing the femoral portion of the hip joint, the acetabulum portion of the hip joint may also require replacement. If the acetabulum also needs to be replaced or repaired, all the remnants of the articular cartilage are generally removed from the acetabulum and an acetabular prosthesis which will accommodate the head or ball of the hip prosthesis is affixed to the acetabulum. It is generally known in the art to affix the acetabular prosthesis to the acetabulum by means of cement, screws, or other appropriate fixation mechanisms.
A typical acetabular prosthesis generally includes two (2) modular portions. In particular, the modular portions include an acetabular cup or shell and a synthetic liner or bearing wherein the liner is affixed within the acetabular cup through a locking mechanism. The modular acetabular prosthesis allows for numerous liners to be produced for a singular acetabular cup or vice versa. Other modular attachments may include additional fixation mechanisms to affix the acetabular cup to the patient. This enables a surgeon performing the procedure to determine which would fit best for the particular patient. Although a modular acetabular prosthesis performs its job adequately, it would be desirable to have an acetabular prosthesis with an acetabular cup and a liner which does not allow any movement relative to each other once implanted into the bone.
If the acetabular cup and the liner move, such as by micromotion, wear material may result. This wear material may migrate out of the acetabular cup or may enter into the articulating area of the hip joint prosthesis. Over time, these foreign materials may cause additional wearing beyond what is desirable in the acetabular prosthesis. Because of the wear material, it may also be desirable to have an acetabular prosthesis that does not include bores through the acetabular cup. The bores, which generally accept screws or other fixation devices, also allow foreign material or body fluids into the acetabular cup and wear material out of the acetabular cup, which may cause additional or accelerated degeneration of the acetabular prosthesis.
Therefore, it is desirable to provide a substantially non-modular acetabular prosthesis, such as an acetabular prosthesis which improves upon existing modular acetabular prostheses and does not suffer from the above mentioned disadvantages.
In accordance with the teachings of the present invention, a method and apparatus for providing a substantially non-modular acetabular cup which may include additional modular or non-modular flanges for use in orthopedic surgery is disclosed. The shell portion of the acetabular cup may be formed from a ceramic material that includes three integrally formed regions. In particular, a ceramic shell having an inner and outer porous region and therebetween a non-porous region. A liner may then be interdigitated into the inner porous region of the shell to be held firmly in place. The acetabular prosthesis is then placed into the bone of the ileum and the outer porous region allows bone to regrow to hold the acetabular prosthesis in place. When the shell is made of ceramic, the ceramic material is placed in a mold and then sintered to form the shell of the acetabular prosthesis. The bearing liner is formed by placing a polymer powder in the shell and through heat and pressure, is melted and formed into a solid bearing liner which interdigitates into the interior porous region of the shell of the acetabular prosthesis.
In a first embodiment, an acetabular prosthesis includes a rigid exterior shell that forms the acetabular cup and a bearing liner is formed and interdigitated on the inside, which include the regions that overlay the top edge of the cup.
In another embodiment, the bearing liner formed on the inside of the acetabular cup protrudes at an angle from the opening of the acetabular cup. In particular, the bearing liner would then allow the hip joint to have an angle which is different from the implantation angle of the acetabular cup.
In yet another embodiment, the bearing liner extends a distance above the outer edge of the ceramic portion of the acetabular cup. In particular, the bearing liner creates a wall along the edge of the acetabular cup in a specific arcuate region. The wall creates an arcuate region in which the hip bone would not be able to rotate within the prosthesis.
In yet another embodiment, the non-porous middle region of the acetabular cup extends through and creates an upper collar above and around the outer and inner porous regions. Further formed in the collar are holes or indents to accept an impacter instrument. The impacter instrument is used to align the acetabular prosthesis during the surgical procedure and hold the instrument in place while the acetabular prosthesis is impacted into the bone portion.
In yet another embodiment, an upper collar of non-porous material extends down and over the outer porous region to provide fins which help align the acetabular prosthesis when it is being implanted into the bone. The fins allow the acetabular prosthesis to be placed properly in the acetabulum to receive the ball of the femur to form the hip joint.
In yet another embodiment, non-porous material extends through the bottom of the acetabular cup. That is, portions of the non-porous material extend through the outer porous region to form spikes near the bottom of the acetabular cup. These spikes formed by the non-porous material help secure the acetabular prosthesis in its final implanted position. In this way, a minimum amount of cement or other holding materials may be necessary to ensure that the acetabular prosthesis is affixed in the proper position.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.